The present invention relates to electrodes for electrochemical processes, and particularly electrodes composed of a relatively inert metallic support at least an outer layer of which is made of titanium or a titanium alloy and optionally containing a core of a better conducting metal, for example copper, iron, aluminum or an alloy of these metals and a protective coating with electrocatalytic properties containing at least one noble metal and/or an oxide thereof.
The electrodes according to the present invention can be used in various electrochemical processes, such as cathodic protection, desalination or purification of water, electrolysis of water or hydrochloric acid, production of current in a fuel cell, reduction or oxidation of organic compounds or the electrolytic manufacture of persalts, but they are particularly useful as anodes in the electrolysis of aqueous solutions of alkali metal halides, particularly sodium chloride, in both diaphragm cells and mercury cells, where they catalyze the discharge of chloride ions which takes place at a remarkably low and practically constant overpotential throughout the life of the electrode. Under the conditions existing in the cell, the rate of wear of such anodes is negligible, which means that they have a practically unlimited life and eliminate the laborious operation of opening the cell and replacing the electrodes.
Although known electrodes are remarkably resistant to electrochemical attack in a good number of corrosive media, the substrate made of titanium or titanium alloy is nevertheless not completely inert, particularly used as an anode support in the electrolysis of aqueous solutions of alkali metal chlorides, where they suffer subsurface corrosion by the chlorinated brine which infiltrates through bare patches, pores, or fissures present in the conventional coatings. This in time inevitably causes detachment of the coating from its substrate through localized peeling, thus appreciably increasing the overpotential for liberation of chlorine and thereby reducing the effective life of the electrode, which sooner or later will have to be replaced.